The invention relates to a method for manufacturing a press felt with a seam, in which method a base fabric of the press felt is woven of several machine direction and cross-machine direction yarns, and at least part of the machine direction yarns are arranged to form seam loops to the cross-machine direction connecting edges of the base fabric. The seam loops can be arranged to overlap on the press section, whereby one or more seam yarns connecting the connecting ends can be arranged to the formed seam loop channel. Further, after weaving, one or more batt fibre layers are fastened to the base fabric at least on its web-side surface to make the structure denser.
The invention also relates to a press felt and its base fabric. The subject matters of the invention are defined in more detail in the preambles of the independent claims.
Press felts are used in a press section of a paper machine so that water in the web to be dried may penetrate into them. Depending on the structure of the press, the press felt may be arranged either on one side or on both sides of the web to be dried. The purpose of the press felt is after pressing to transport the water along in such a manner that it cannot re-enter the web. During pressing, the paper web is transported on the felt to a gap, or nip, between two rolls. The structure of the felt should be made so that in the nip, water is able to transfer easily from the web to the felt. Press felts comprise a base fabric that, among other things, provides the felt with the necessary water volume. To make the felt surface smooth, batt fibre is fastened at least to the web-side surface of the base fabric. The base fabric is typically made by weaving in a weaving machine.
It is further possible to form seam loops at the ends of the press felt during weaving so as to produce a press felt in the form of a closed loop by connecting the connecting ends. Mounting such a press felt with a seam onto a paper machine is in general easier and faster than mounting a press felt that is already in the form of a closed loop. The yarns making up the seam loops are relatively thick so as to provide sufficient tensile strength for the seam and so that the handling of the loops is easy while connecting the seam. However, the weaving points and seam loops of thick yarns of this type may cause marking on the web. Therefore, it is known to arrange a surface layer on the web-side surface of the web. However, present surface layers are not able to prevent the marking caused by the thick yarns that form the seam loops in a desired manner, which is why it is necessary to use a large number of batt fibres. A felt with a great deal of batt fibres tends to block. A problem thus arises from the insufficient ability of the present surface layers to protect the part of the bottom layer comprising the seam loops so as to avoid marking.